Should I buy a diesel car? Everything you need to know

Some important changes are taking place that could affect owners of diesel cars. We round up everything you need to know if you own a diesel or are thinking of buying one

Words ByClaire Evans

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12 Jul 2017 16:00Last updated: 13 Sep 2017 09:26

There appears to have been a massive U-turn in the official opinion on diesel cars. They have gone from being the most favoured – and financially incentivised – models to some of those hit hardest by punitive levels of taxation.

The latest development is the announcement by the government that only fully electric cars and vans will be sold in the UK by 2040. The move is part of a long-term strategy to combat air pollution, which the government says is linked to 40,000 premature deaths a year.

A scrappage scheme to help owners of older, higher-polluting diesels is also expected, although this isn't likely to be announced until a consultation has been held to determine the best way of doing this.

So should you shun diesel cars or is it still okay to buy one? We consider the background of the diesel engine story and look at the implications for existing owners and those considering buying a diesel.

Why has the Government turned against diesels?

Diesel-engined cars were promoted by successive UK governments for more than a decade because they have, on average, 20% lower CO2 emissions and 20% better official fuel economy than their petrol counterparts. These are important factors in helping to tackle climate change. Drivers appreciated the lower road tax (VED) and company car tax that were applicable to diesels and their popularity grew. Today, there are more than 10 million diesel cars on our roads and they account for almost half of the new cars registered each year.

However, the Government now needs to address the levels of pollution in our cities because it is being sued by the European Commission for repeatedly breaching air pollution limits. The announcement of the ban on petrol and diesel-engined cars from 2040 is part of a £3bn plan to tackle air pollution in response to the legal action.

The nitrogen oxides (NOx) produced by diesel engines are one cause of air pollution. So, as well as announcing the introduction of extra charges for the oldest, highest-polluting diesels if they’re driven in urban areas at peak times, the Government has changed the road tax banding system for new cars so that, after the first year, owners of petrol and diesel cars will pay the same rate.

Another reason for the change in road tax is that around a quarter of new cars being registered have emissions of 99g/km or less, so they qualified for free road tax under the previous system. While this demonstrates the improvements car makers have made in reducing CO2 emissions, it also means the Government has been raising far less in road tax.

How polluting are diesel cars?

Although diesel-engined cars emit more particulates than petrol ones, their CO2 emissions are generally lower. It’s also important to note that older diesels have far higher particulates and CO2 emissions than newer ones and that the European Union has been tightening up on emissions since 1992.

The first Europe-wide emissions standards, applicable to all new cars registered from January 1993, set an upper limit of 2.72g/km of carbon monoxide (CO) and 0.97g/km of NOx for diesel engines.

Significant improvements were made with the Euro 5 standard that applies to cars registered after January 2011. In order to comply with the limit of 0.18g/km of NOx, diesel-engined cars had to be fitted with diesel particulate filters (DPFs) that capture 99% of all particulate matter before it escapes out of the exhaust.

The latest diesel-engined cars (those sold from September 2015 onwards) comply with Euro 6 regulations and are the cleanest in history. As well as being fitted with DPFs, they have systems that convert most of the NOx from the engine to largely harmless nitrogen and water; for diesel engines, their NOx emissions cannot exceed 0.08g/km.

How has car tax changed?

Until recently, cars with CO2 emissions of 99g/km or less qualified for free road tax. However, from 1 April this year, new rates of car tax were introduced, meaning that only zero-emissions cars costing less than £40,000, such as pure electric models, are free to tax. The first-year rate is still dependent on CO2 emissions and ranges from £10 for cars with a CO2 output of 1-50g/km to £2000 for those with more than 255g/km. After that, a flat rate of £140 per year is payable on cars costing less than £40,000.

Hybrid vehicles qualify for a £10 reduction in annual fees, but buyers of all vehicles costing more than £40,000 (including fully electric ones) have to pay an additional annual fee of £310 in years two to six. This change only applies to new cars registered on or after 1 April; it doesn’t affect cars registered before that date. So, if you buy a second-hand diesel car with 99g/km of CO2 emissions, it will still qualify for free road tax.

What other charges do diesel car owners face?

In London, drivers of diesel and petrol cars first registered before 2006 that do not meet Euro 4 NOx standards will have to pay the Toxicity Charge, or T-Charge, from 23 October 2017. It is an additional fee of £10 that will be payable for vehicles entering the current Congestion Charge zone 24 hours a day, every day of the year.

In April 2019, a new Ultra Low Emission Zone (ULEZ) will be created in the capital to replace the T-Charge. Once it’s in operation, drivers of diesel vehicles that do not meet Euro 6 emissions standards and petrol vehicles that do not comply with Euro 4 standards will have to pay an extra £12.50 to drive through certain parts of London. It will affect diesel cars registered before September 2015 and petrols registered before 2006.

Other cities around the UK are expected to follow London’s lead with the scheme.

What’s being done to help diesel car owners cope with the extra costs?

Although there will be no assistance with the cost of road tax on new diesel cars, the Government has said it will aim to help owners of diesels living inside the ULEZ and other areas where low-emissions zones are introduced.

There are no official details yet about what form that assistance might take, but it is believed that a diesel scrappage scheme will be introduced to encourage owners to trade in higher-emissions diesels for cleaner models.

What about other European cities?

There are more than 200 low-emissions zones in cities throughout Europe so, if you’re thinking of driving abroad, check such schemes along your planned route and at the destination.

Paris is among the most recent to introduce a scheme to combat air pollution. Its Air Quality Certificate scheme bans cars first registered before 1997 from entering the city between 8am and 8pm on weekdays. It also bans motorcycles first registered before 2000 and buses and HGVs built before 2001.

Newer vehicles are rated on their emissions and will qualify for one of six different coloured windscreen stickers that will allow access to the city inside the Périphérique ring road.